What is SDH technology?What does SDH mean

SDH technology is based on the basic concept of synchronous transmission module (STM-1, 155Mbit S), which is an optical fiber transmission system, which is compatible with various PDH systems by using virtual containers. SDH transmission network has the advantages of intelligent routing and configuration capabilities, convenient upper and lower circuits, strong maintenance, monitoring and management capabilities, and unified optical interface standards. SDH is equivalent to a transparent physical channel, on this transparent channel, as long as the bandwidth allows, users can carry out various services, such as **, data, digital, etc., and the quality of the service will be strictly guaranteed.

Compared with the traditional PDH technology, SDH technology has the following obvious advantages: —1. Unified bit rate: —In PDH, there are three rate levels in the world: Europe, North America and Japan.

A uniform bit rate is achieved in SDH. In addition, a uniform standard for optical interfaces is specified, thus making it possible to interconnect devices from different manufacturers. —2. Strong network management ability:

The SDH frame structure specifies a rich number of NMS bytes, which provide the ability to meet various requirements. —3. Self-healing protection ring: - The SDH equipment can also form a ring network with self-healing protection ability, which can effectively prevent the transmission medium from being cut off and the communication service being terminated.

4. Byte multiplexing technology used in SDH technology: - If the main difference between SDH technology and PDH technology is compared with railway transportation, PDH technology is like a bulk train, all kinds of goods (business) are piled up in the carriage, if you want to take off a package of specific goods (a certain transmission business) at a certain station, that is, you need to unload all the goods on the car first, find the goods you need, and then pile the remaining goods and the new goods at the station one by one to the car and transport them away. Therefore, PDH technology needs to be equipped with a large number of multiplexing equipment of various subgroups wherever upper and lower circuits are required.

SDH technology is like a container train, where all kinds of goods (operations) are labeled (various overheads) and loaded into containers.

Synchronize the digital system.

SDH (Synchronous Digital Hierarchy), as defined by ITU-T recommendations, is a digital signal of different rates.

The transmission provides a technical framework consisting of a corresponding level of information structure, including multiplexing methods and mapping methods, as well as related synchronization methods.

SDH Applications:

Due to the numerous characteristics of SDH mentioned above, it makes it useful in the WAN.

The field and the field of private networks have developed enormously. China Mobile, China Telecom, China Unicom, Radio and Television and other telecom operators.

Large-scale SDH-based backbone optical transmission networks have been built.

Use the large-capacity SDH loop to carry IP services and ATM services, or directly lease them to Duanjian enterprises and institutions in the form of leased circuits. Some large-scale private networks also adopt SDH technology to set up SDH optical loops within the system to undertake various services on the baseload. For example, the power system.

For units where networking is more urgent and there is no possibility of erecting a dedicated SDH loop, many of them have adopted the method of renting telecom operator circuits. Since SDH is based on the physical layer.

The unit can carry a variety of services on the leased power road without the limitation of transmission.

There are many bearer modes, such as multi-service multiplexing with integrated multiplexing devices based on TDM technology, or packet switching of multi-service services with IP-based devices. SDH technology can truly realize the bandwidth guarantee of leased circuits, and it is also better than VPN and other methods in terms of security.

In the first institutions and enterprises that pay great attention to security, SDH leased lines have been widely used. Generally speaking, SDH can provide interfaces such as E1, E3, STM-1, or STM-N (N=4, 16, 64) to meet various bandwidth requirements. At the same time, it has also been accepted by most units.

The above content reference: Encyclopedia-SDH

SDH (Synchronous Digital Hierarchy), defined according to the ITU-T recommendations, is a technical system composed of information structures that provide corresponding levels for the transmission of digital signals at different rates, including multiplexing methods and mapping methods, as well as related synchronization methods.

Due to the multiple network topologies of SDH, the network is very flexible, which can enhance the functions of network monitoring, operation management and automatic configuration, optimize the network performance, and also make the network run flexibly, safely and reliably, so that the network functions are very complete and diversified.

The information structure level adopted by SDH is called synchronous transport module STM N (Synchronous transport, N=1,4, 16,64), the most basic module is STM 1, four STM 1 synchronous multiplexing constitutes STM 4, and 16 STM 1 or four STM 4 synchronous multiplexing constitute STM 16;SDH adopts a block-like frame structure to carry information, each frame is composed of 9 vertical rows and 270 N horizontal columns of bytes, each byte contains 8 bits, the whole frame structure is divided into three areas: section overhead (SOH) area, STM N net load area and management unit pointer (AU PTR) area, in which the segment overhead area is mainly used for network operation, management, maintenance and assignment to ensure that the information can be transmitted normally and flexibly, and it is divided into regeneration segment overhead (rege). Nerator Section Overhead (RSOH) and Multiplex Section Overhead (MSOH); The net load area is used to store the bits that are really used for information services and a small number of channel overhead bytes used for channel maintenance and management. The snap-in pointer is used to indicate the exact position of the first byte of information within the net load area within the STM n frame, so that the net load can be properly separated when received. The transmission time of each frame is 125 s, and 1 125 1000000 frames are transmitted per second, and the bytes per frame are 8 bits (9 270 1) = 19440 bits, so the transmission rate of STM 1 is 19440 8000=; The transmission rate of STM 4 is 4; STM 16 has a transmission rate of 16 or 4.

When SDH transmits service signals, the frames of various service signals to enter SDH must go through three steps: mapping, positioning and multiplexing: mapping is the process of loading signals of various rates into the corresponding standard container (C) after code speed adjustment, and then adding channel overhead (POH) to form a virtual container (VC), and the deviation of the frame phase is called frame offset; Positioning is the process of collecting the frame offset information into the branch unit (TU) or management unit (AU), which is realized by the function of the branch unit pointer (tu ptr) or the management unit pointer (AU ptr); Multiplexing is the process of adjusting the signal of multiple low-cost channel layers to enter the ** channel through the code speed adjustment or the signal of the multiple ** channel layers to enter the multiplexing layer through the code speed adjustment.

As a five-year SDH experience, I can't explain the SDH principle to you within a thousand, you can find the textbook on the Internet. To put it mildly, SDH is a synchronous number system, so keep in mind that a synchronization system has a frame rate of 8000 at different rate levels. The frame structure is similar to a 9*270*n block frame, which contains overhead (maintenance information) and net load, and the frame structure and overhead bytes are to be remembered.

Secondly, it is necessary to remember the SDH packaging process and maintain the signal generation process. Above.

SDH (Synchronous Digital Transmission System) is developed based on PDH (Quasi-Synchronous Digital Transmission System), which improves PDH's unfavorable large-capacity transmission and has a unified network management interface standard in the world. With byte interpolation and flexible mapping, it has very powerful OMA (Open Mobile Architecture) capabilities!

Synchronous digital transmission mechanism, which is the most basic technology in optical transmission networks.

The SDH system can directly descend low-speed signals (e.g., 2Mbit S) from high-speed signals (e.g., STM-1), eliminating the need for multi-level multiplexing and demultiplexing processes. The realization of this function is completed by the pointer mechanism, and the function of the pointer is to indicate the position of the low-speed signal at all times, so that the required low-speed signal can be correctly split when "unpacking", so as to ensure the realization of the function of SDH directly from the high-speed signal to the low-speed signal. It can be said that the pointer is a major feature of SDH.

But the implementation of the pointer function adds complexity to the system. The most important thing is a type of jitter that is unique to SDH in the system—the binding jitter caused by pointer adjustment. This kind of jitter mostly occurs at the network boundary (SDH PDH), and its low frequency and amplitude will lead to the deterioration of the performance of low-speed signals after tearing out, and it will be quite difficult to filter out this jitter.

3) The impact of a large number of software on system security SDH is characterized by the high degree of automation of OAM, which also means that software occupies a considerable proportion of the system, which makes the system vulnerable to computer viruses, especially in today's ubiquitous computer viruses. In addition, human error operation and software failure at the network layer can also have a fatal impact on the system. In this way, the security of the system becomes a very important aspect.

SDH system is a new thing, although there are still such and such defects, but it has been in the development of the transmission network, showing a strong vitality, the transmission network from PDH to SDH has been an inevitable trend.

2.There is a standardized hierarchy of information structures, which are called synchronous transmission patterns. 3.

It has abundant bits for maintenance and management in the frame structure, so it has a powerful network management function.

SDH stands for Synchronous Digital Transmission System, which is a transmission protocol. SDH is a transmission system that regulates the frame structure, multiplexing mode, transmission rate, interface, code pattern and other characteristics of digital signals.

I don't know how it works, but you can search for a lot of information about SDH technology on the Internet, and give you a vernacular explanation of SDH here, I hope it will help you understand:

SDH can be simply understood as container transportation.

Take the 2M service as an example. Every 2m business is a piece of goods. The goods were first packed in a standard box (VC12) and then attached to the box with an identification label indicating its location (TU-12), then three of these labeled boxes were packed in a larger box (TUG2), seven large boxes were packed in a larger box (TUG3), and three larger boxes were packed in a single crate (VC4).

A container carrier (STM-1) is then formed by adding some additional information (segment overhead and pointers) about the individual boxes in the box to the container. Multiple container carriers can also be combined to form a longer container carrier fleet (STM-N). Such a fleet of containers travels on a highway made of fiber optics, transporting goods.

At the receiving end of the goods, the goods (2m business) are taken out in the opposite way above.

The specifications of each box in the above example are unified and standard, that is to say, as long as the equipment of any manufacturer is packed in boxes according to this specification, then the goods can be transported normally. That's what SDH means.

Located in the transport layer, it is to put the user's data signal on the transport layer network for transmission, because the transport layer network bandwidth is large and stable.

(1) SDH transmission system has a unified frame structure digital transmission standard rate and standard optical path interface in the world, so that the network management system can communicate with each other, so it has good horizontal compatibility, it can be fully compatible with the existing PDH, and accommodate a variety of new service signals, forming a global unified digital transmission system standard, improving the reliability of the network.

2) The different levels of code streams of the SDH access system are arranged very regularly in the net load area of the frame structure, and the net load is synchronized with the network, and it uses the software to directly interpolate the high-speed signal from the low-speed branch signal at one time, so as to realize the characteristics of one-time multiplexing.

It overcomes the process of decomposing all high-speed signals step by step and then reusing them in the PDH quasi-synchronous multiplexing mode, which greatly simplifies the DXC and reduces the back-to-back interface multiplexing equipment, improving the service transmission transparency of the network.

3) Due to the use of more advanced add/drop multiplexer, digital cross-connection, network self-healing function and reorganization function, it is very powerful, with a strong survival rate.

Because the SDH frame structure arranges 5% of the overhead bits of the signal, its network management function is particularly powerful, and can form a unified network management system, which plays a positive role in the automation, intelligence, channel utilization, and reduction of network maintenance costs and survivability.

4) Due to the various network topologies of SDH, the network it composed of is very flexible, which can enhance the functions of network monitoring, operation management and automatic configuration, optimize the network performance, and also make the network run flexibly, safely and reliably, so that the functions of the network are very complete and diversified.

5) SDH has the performance of transmission and switching, and the composition of its series of equipment can be freely combined through the function blocks, to achieve different levels and various topology of the network, which is very flexible.